Introduction
This study compared the skeletal and dental changes of microimplant assisted rapid palatal expansion (MARPE) with those produced by surgically assisted rapid maxillary expansion (SARPE) in postpeak adolescents and adults.
Methods
The sample comprised 17 patients (mean age, 26 ± 11 years) selected for the MARPE group and 15 (mean age, 28.5 ± 10.5 years) selected for the SARPE group. Cone-beam computed tomography scans taken just before and after the expansion were used to assess dental and skeletal changes and compare the changes between the groups.
Results
MARPE showed greater transversal skeletal changes in the midface and posterior and anterior maxillary base measurements. The transverse displacement of the alveolar process was greater but not significant for the SARPE group than the MARPE group. Regarding dental effects, the root distance measurements did not differ between the groups, but SARPE produced a significantly greater increase in intermolar and interpremolar distance and a greater buccal inclination of the alveolar process and supporting teeth than MARPE.
Conclusions
The MARPE technique showed an increase in skeletal transverse maxillary expansion at the midface and basal bone compared with SARPE, especially at the posterior palatal region; however, no difference was found in the expansion of the alveolar process between the 2 methods. MARPE presented a more parallel expansion in both a coronal and axial view, whereas SARPE led to a V-shaped opening. The greater buccal inclination of the alveolar process and supporting teeth was observed in the SARPE group.
Highlights
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Microimplant assisted rapid palatal expansion produced better skeletal changes.
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Microimplant assisted rapid palatal expansion produced a more parallel expansion.
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Surgically assisted rapid palatal expansion produced a V-shaped opening.
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Surgically assisted rapid palatal expansion produced greater dentoalveolar changes.
Treatment of transverse maxillary constriction using rapid palatal expansion (RPE) is most indicated in mixed dentition until adolescence during growth. RPE prognosis is related to the level of maxillary suture interdigitation, and its effect is inversely related to the success of the expansion; that is, the greater the interdigitation and more numerous the synostoses presented at the sutures, the lower the chances of splitting the maxilla without surgical intervention, known as surgically assisted rapid palatal expansion (SARPE). ,
In young adults and postpeak growth adolescents presenting skeletal maturity, the results of nonsurgical RPE may vary considerably. One study showed high success in young adults achieving a moderate expansion, whereas others found that age limited the RPE success rate in females aged up to 18 years and males aged up to 21 years. In patients aged more than 18 years, the skeletal effects are insignificant, exhibiting more dentoalveolar expansion of the maxillary arch.
Complications have been reported in the literature as a consequence of conventional tooth-borne RPE devices, including pain and swelling during expansion, buccal root resorption of the supporting teeth, buccal cortical and bone resorption, and bone dehiscence. Other authors reported patients with ischemia and necrosis in the palate mucosa when maxillary sutures do not respond to orthopedic forces applied through a tooth-supported expander.
The reason for the conventional RPE failures may be due to greater rigidity in craniofacial structures in skeletally mature patients. Therefore, SARPE is indicated to treat transverse maxillary deficiency in adult patients. Unfortunately, this treatment is often rejected because it is an invasive surgical procedure, with risks and high costs for the patient.
Miniscrews were recently developed for use as anchorage supporting orthopedic forces. , A microimplant assisted rapid palatal expansion (MARPE) technique has been advocated to optimize force distribution to the maxillary basal bone and circummaxillary structures, enhancing skeletal effects and minimizing dental inclination , , ; therefore, preserving periodontal health. , A recent clinical study showed that out of 69 patients treated using MARPE, 9 had failed to split midpalatal sutures (an 86.96% success rate) in young adults (mean age, 20.9 ± 2.9 years). Thus, because of this therapy’s high success rate, it may be recommended as an alternative to surgical expansion.
This study compared the skeletal and dental changes of MARPE with those produced by SARPE in patients with bone maturity. We believe that this information will help clarify the transversal changes achieved in both treatment modalities to better guide orthodontists to decide which method provides the most benefit to individual patients.
Material and methods
This clinical study was previously approved by the Research Ethics Committee of the Faculty of Dentistry of Araraquara of São Paulo State University (CCAAE Nos. 60393416.7.0000.5416 and 14484713.1.0000.5416).
The overall sample included 2 parallel controlled groups of patients treated for transverse maxillary deficiency using MARPE or SARPE. The MARPE sample consisted of 17 postpubertal adolescent and adults (4 men and 13 women) with a mean age of 22.9 years (minimum, 15; maximum, 37) treated between 2016 and 2019 at the Dental Center of Studies and Research (COESP), João Pessoa, Paraíba, Brazil and São Paulo State University (UNESP), Araraquara, São Paulo, Brazil. The SARPE group corresponded to a sample obtained from the archives of the Residency Program in Oral and Maxillofacial Surgery and Traumatology of Araraquara Dentistry College (UNESP) containing cone-beam computed tomography (CBCT) files (presurgery and postsurgery) of 15 patients (10 women and 6 men) with a mean age of 30.4 years (minimum, 18.7; maximum, 39.7) treated between 2010 and 2012. Patients who had undergone previous orthodontic treatment and who had severe facial deformities or syndromes were excluded. Selection criteria for both groups were transverse maxillary deficiency greater than 4 mm associated with unilateral or bilateral crossbite ( Table I ). The MARPE device used in this study had a 9-mm jackscrew expander and 4 miniscrews inserted paramedian to the midpalatal suture (Peclab, Belo Horizonte, Minas Gerais, Brazil) ( Fig 1 ). MARPE positioning was planned using initial CBCT images (T0) so that the miniscrews were inserted in a region of adequate bone thickness. After successful expansion, the patients underwent a second CBCT examination (T1).
| Group | n | Mean | SD | P ( t test) |
|---|---|---|---|---|
| MARPE | 17 | −6.00 | 2.34 | 0.185 ∗ |
| SARPE | 15 | −7.26 | 2.93 |
The miniscrews were installed manually with a contra-angle driver (Peclab), and the torque was measured between 15 N and 20 N. Activation protocol was a 2/4 turn immediately after mini-implant placement, and 2/4 turns daily on the following days (from 14 to 18 days) until full correction was achieved.
The SARPE group underwent surgery, including LeFort I subtotal osteotomy in the lateral wall of the maxilla, pterygomaxillary suture, and midpalatal suture disruption performed under general anesthesia at the university medical hospital. A hyrax expander was used with an activation protocol of 1/4 turns (0.2 mm) 2 times daily until crossbite correction.
CBCTs at T0 and T1 with MARPE and SARPE were obtained using an i-CAT Next Generation (Imaging Sciences International, Hatfield, Pa) at these settings: 120 kVp; 36 mA; 0.25-mm voxel size; scan time, 7 seconds; and field view of 13 cm in height × 16 cm in depth. For both groups, the data were exported in the Digital Imaging and Communication in Medicine format and analyzed using NemoStudio software (Nemotec, Madrid, Spain). For sample blinding, examiner A (P.A.) coded the CBCT files, and examiner B was responsible for skeletal and dental measurements.
The images in 3-dimensional reformatting were positioned according to 3 spatial orientation planes (sagittal, coronal, and axial), as shown in Figure 2 .
To measure the skeletal effects of expansion in both groups, linear measurements (in millimeters) of the maxillary bone structure were obtained in the upper and lower segments of the maxilla and the anterior and posterior segments to quantify the transverse changes in the nasal cavity and evaluate the maxillary split pattern. To evaluate the dental results, measurements were obtained to quantify the amount of expansion and inclination ( Fig 3 and Table II ).
| Measurements | Abbreviation | Description |
|---|---|---|
| Skeletal measurements | ||
| Axial slice passing through the infraorbital foramina | MIF | Distance between the infraorbital foramina |
| Axial slice passing through the palatine processing center | PP | Distance between the greater palatine foramina |
| AP | Distance between the lateral walls of the incisive foramen | |
| Coronal slice passing through the maxillary right first molar root apex | MMW | Distance between the lateral maxilla walls at the plane that passes on the nasal floor |
| MNW | Maximum width of the nasal cavity | |
| MAW | Greater distance between the maxillary buccal alveolar processes | |
| Coronal slice passing through the maxillary right first premolar root apex | PMW | Distance between the lateral maxilla walls at the plane that passes on the nasal floor |
| PNW | Maximum width of the nasal cavity | |
| PAW | Greater distance between the maxillary buccal alveolar processes | |
| Dental measurements | ||
| Coronal slice (multiplanar reconstruction to locate each reference point used in dental measurements) | IMR | Distance between the apex of the palatal roots of the molars |
| IMC | Distance between the buccal middle molar cusps | |
| RMA | Angle between the cusp-apex line of the right molar and the horizontal plane | |
| LMA | Angle between the cusp-apex line of the left molar and the horizontal plane | |
| IPR | Distance between the apex of the palatal roots of the premolars | |
| IPC | Distance between the buccal middle premolar cusps | |
| RPA | Angle between the cusp-apex line of the right premolar and the horizontal plane | |
| LPA | Angle between the cusp-apex line of the left premolar and the horizontal plane |
Statistical analysis
To determine the intraexaminer error, 40% of the CBCT scans were reanalyzed randomly by the same examiner within a 2-week interval. The reproducibility of the method was evaluated using the intraclass correlation test and a paired t test for the linear and angular measurements. The intraclass correlation of the linear and angular measurements was greater than 0.92. The paired t test showed that the mean variation in the angular measurements was 0.20 and for the linear measurements was a maximum of 0.14 mm, indicating excellent intraexaminer reliability.
Shapiro-Wilk and Levene tests verified the normality of the data distribution and homogeneity of variances, respectively. The data are shown as the mean and standard deviation of the variables with a normal distribution.
RPE using MARPE and SARPE were compared before and after treatment using a Student t test for dependent samples. The Student t test for independent samples was used to evaluate differences between the MARPE and SARPE groups.
Statistical analysis was performed using SPSS for Windows (version 16.0; SPSS, Chicago, Ill) with a significance level of 5% (α = 0.05).
Results
A significant difference in all skeletal measurements was found after maxillary expansion with MARPE ( P <0.05). The SARPE results showed a significant change after expansion in the majority of the skeletal measurements ( P <0.05), with the exception of the midfacial width and posterior maxillary base ( Table III ). MARPE showed significantly greater expansion in the midfacial area, nasal cavity, anterior and posterior palate, and posterior maxillary base than SARPE. No statistically significant difference was found for expansion between MARPE and SARPE at the level of the alveolar process and anterior maxillary base ( Table III ).
| Area of interest | Measurement | MARPE (n = 17) | SARPE (n = 15) | MARPE − SARPE | Comparisons | ||||||
|---|---|---|---|---|---|---|---|---|---|---|---|
| Mean | SD | P | Mean | SD | P | Mean | SEM | P ( t test) | |||
| Skeletal | |||||||||||
| Midfacial area (mm) | MIF | 2.90 | 1.20 | <0.001∗ | 0.21 | 0.37 | 0.051∗∗ | 2.70 | 0.31 | <0.001∗ | MARPE > SARPE |
| Posterior palate (mm) | PP | 2.75 | 0.85 | <0.001∗ | 0.89 | 0.63 | <0.001∗ | 1.86 | 0.27 | <0.001∗ | MARPE > SARPE |
| Anterior palate (mm) | AP | 3.69 | 1.42 | <0.001∗ | 2.53 | 1.48 | <0.001∗ | 1.16 | 0.51 | 0.031∗ | MARPE > SARPE |
| Posterior maxillary base (mm) | MMW | 2.27 | 1.10 | <0.001∗ | 0.11 | 0.63 | 0.513∗∗ | 2.16 | 0.31 | <0.001∗ | MARPE > SARPE |
| Posterior nasal cavity (mm) | MNW | 2.92 | 1.13 | <0.001∗ | 1.10 | 0.80 | <0.001∗ | 1.82 | 0.35 | <0.001∗ | MARPE > SARPE |
| Posterior alveolar process (mm) | MAW | 3.86 | 1.20 | <0.001∗ | 4.05 | 1.46 | <0.001∗ | −0.19 | 0.47 | 0.694∗∗ | MARPE = SARPE |
| Anterior maxillary base (mm) | PMW | 3.26 | 2.58 | <0.001∗ | 2.74 | 1.80 | <0.001∗ | 0.52 | 0.80 | 0.518∗∗ | MARPE = SARPE |
| Anterior nasal cavity (mm) | PNW | 2.89 | 2.04 | <0.001∗ | 0.95 | 1.56 | 0.033∗ | 1.94 | 0.65 | 0.005∗ | MARPE > SARPE |
| Anterior alveolar process (mm) | PAW | 4.30 | 1.87 | <0.001∗ | 5.05 | 1.96 | <0.001∗ | −0.75 | 0.68 | 0.277∗∗ | MARPE = SARPE |
| Dental | |||||||||||
| U6 root distance (mm) | IMR | 3.81 | 1.55 | <0.001∗ | 3.31 | 1.21 | <0.001∗ | 0.49 | 0.50 | 0.326∗∗ | MARPE = SARPE |
| U6 cusp distance (mm) | IMC | 5.25 | 2.34 | <0.001∗ | 7.91 | 2.00 | <0.001∗ | −2.66 | 0.78 | 0.002∗ | MARPE < SARPE |
| U6 right angulation (°) | RMA | 2.87 | 1.94 | <0.001∗ | 7.78 | 4.05 | <0.001∗ | −4.91 | 1.15 | <0.001∗ | MARPE < SARPE |
| U6 left angulation (°) | LMA | 3.39 | 2.41 | <0.001∗ | 6.82 | 3.76 | <0.001∗ | −3.43 | 1.10 | 0.004∗ | MARPE < SARPE |
| U4 root distance (mm) | IPR | 4.03 | 1.76 | <0.001∗ | 4.34 | 1.99 | <0.001∗ | −0.30 | 0.66 | 0.649∗∗ | MARPE = SARPE |
| U4 cusp distance (mm) | IPC | 5.21 | 2.25 | <0.001∗ | 7.19 | 2.47 | <0.001∗ | −1.98 | 0.84 | 0.025∗ | MARPE < SARPE |
| U4 right angulation (°) | RPA | 1.40 | 1.74 | 0.004∗ | 4.71 | 3.98 | <0.001∗ | −3.31 | 1.11 | 0.008∗ | MARPE < SARPE |
| U4 left angulation (°) | LPA | 1.88 | 2.33 | 0.004∗ | 4.60 | 3.61 | <0.001∗ | −2.72 | 1.06 | 0.016∗ | MARPE < SARPE |
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